In Unexamined Published Japanese Patent Application (Kokai) No. Hei 1-92504or Unexamined Published Japanese Utility Model Application (Kokai) No. Hei 2-50105, for example, there is disclosed a valve timing control device comprising: a rotational transmitting member mounted around a valve opening and closing rotary shaft assembly (including a cam shaft and an internal rotor integrally mounted on the cam shaft) rotatably assembled with the head of an internal combustion engine so as to rotate relative thereto within a predetermined range for transmitting rotating power from a crank pulley; vanes provided on the rotary shaft assembly; fluid chambers formed between the rotary shaft assembly and the rotational transmitting member and halved into advancing chambers and delaying chambers by the vanes; first fluid passages for supplying and discharging a fluid to and from the advancing chambers; second fluid passages for supplying and discharging the fluid to and from the delaying chambers; a refuge hole formed in the rotational transmitting member and accommodating therein a locking pin spring-biased toward the rotary shaft assembly; a fitting hole formed in the rotary shaft assembly for fitting therein a head portion of the locking pin when the rotary shaft assembly and the rotational transmitting member are synchronized in predetermined relative phases; and a third passage for supplying and discharging the fluid to and from the fitting hole.
The valve timing control device, as described in each of the above-cited patent applications is constructed such that the locking pin is moved against the spring-urging force by the fluid supplied to the fitting hole via the third fluid passage. In the case where the fluid supplied to the fitting hole partially leaks through the clearance between the refuge hole and the locking pin to the back pressure chamber accommodating a spring for urging the locking pin, the back pressure chamber may be vented to the atmosphere such that the fluid may be discharged therefrom.
Here, the fluid to be used in the device is a working oil. When the rotating power from the crank pulley is transmitted through a timing chain to the rotational transmitting member, the working oil to be discharged from the back pressure chamber can be employed as the oil for lubricating the timing chain. When the rotating power is transmitted through a timing belt made of a resin or rubber, the working oil may cause a slipping engagement between the timing belt and the rotational transmitting member, or deteriorate the timing belt.